In the past, there is provided a contact device for use in, e.g., an electromagnetic relay, a switch or a timer, which has a magnetic blow structure in which an arc current generated when contact points comes into contact or out of contact with each other is drawn out by a magnetic force of a permanent magnet arranged near the contact points, thereby performing arc extinction.
As one example of the contact device having the magnetic blow structure, there is known a contact device that includes, as shown in FIG. 43, a contact point block 8 formed of a pair of fixed terminals 81 having fixed contact points 811 and a movable contactor 82 having a pair of movable contact points 821 coming into contact and out of contact with the fixed contact points 811, a drive block (not shown) for driving the movable contactor 82 and a plurality of permanent magnets 9 arranged near the contact point block 8 (see, e.g., Japanese Patent No. 3321963).
The movable contactor 82 is formed into a substantially rectangular plate shape. The movable contact points 821 are arranged side by side along the longitudinal direction of the movable contactor 82. As the movable contactor 82 is moved toward the fixed terminals 81 by the drive block, the movable contact points 821 come into contact with the fixed contact points 811.
The permanent magnets 9 are arranged at one and the other lateral sides of the movable contactor 82 so as to oppose to each other across the contact point block 8. In this regard, each pair of the permanent magnets 9 opposing to each other across the contact point block 8 is arranged near each pair of the single fixed contact point 811 and the single movable contact point 821 coming into contact and out of contact with the fixed contact point 811. That is to say, there are provided two pairs of the permanent magnets 9.
Each pair of the permanent magnets 9 is arranged such that the polarities of the mutually-opposing surfaces of the permanent magnets 9 differ from each other. For example, the permanent magnets 9 arranged at one lateral side of the movable contactor 82 (at the upper side in FIG. 43) have N-pole surfaces opposing to the contact point block 8. The permanent magnets 9 arranged at the other lateral side of the movable contactor 82 (at the lower side in FIG. 43) have S-pole surfaces opposing to the contact point block 8. In other words, the permanent magnets 9 arranged at one lateral side of the movable contactor 82 are identical in the polarity of the surfaces opposing to the movable contactor 82. The permanent magnets 9 arranged at the other lateral side of the movable contactor 82 are identical in the polarity of the surfaces opposing to the movable contactor 82. This helps strengthen the magnetic fields flowing across the contact points.
If an electric current flows from one longitudinal side of the movable contactor 82 toward the other longitudinal side (from the left side toward the right in FIG. 43), the arc currents generated when each pair of the contact points comes into contact and out of contact with each other are drawn out away from each other. In other words, the arc current generated at one longitudinal side of the movable contactor 82 (at the left side in FIG. 43) is drawn out toward the one longitudinal side direction. The arc current generated at the other longitudinal side of the movable contactor 82 (at the right side in FIG. 43) is drawn out toward the other longitudinal side direction.
However, if an electric current flows in the reverse direction (from the right side toward the left side), the arc currents generated in the respective pairs of the contact points are drawn out toward each other. For that reason, if an electric current such as a regenerative electric current or the like flows through the contact device in the direction opposite to the normal direction, the arc currents generated in the respective pairs of the contact points make contact with each other. This may possibly lead to short-circuit.
In light of this, there is provided a contact device in which, as shown in FIG. 42, a pair of permanent magnets 9 is arranged at the longitudinal opposite ends of a movable contactor 82 in an opposing relationship across a contact point block 8.
The contact device shown in FIGS. 41 and 42 includes a contact point block 8 formed of a pair of fixed terminals 81 having fixed contact points 811 and a movable contactor 82 having a pair of movable contact points 821 coming into contact and out of contact with the fixed contact points 811, a drive block (not shown) for driving the movable contactor 82 and a pair of permanent magnets 9 arranged near the contact point block 8 (see, e.g., Japanese Patent Application Publication Nos. 2004-71512 and 2008-226547).
The movable contactor 82 is formed into a substantially rectangular plate shape. The movable contact points 821 are arranged side by side along the longitudinal direction of the movable contactor 82. As the movable contactor 82 is moved toward the fixed terminals 81 by the drive block, the movable contact points 821 come into contact with the fixed contact points 811.
The permanent magnets 9 are arranged at one and the other longitudinal ends of the movable contactor 82 in an opposing relationship across the contact point block 8.
In the contact devices disclosed in Japanese Patent Application Publication Nos. 2004-71512 and 2008-226547, the permanent magnets 9 are identical in the polarity of the surfaces opposing to each other. Thus the distribution of the magnetic fluxes formed around one pair of the contact points is symmetrical with the distribution of the magnetic fluxes formed around the other pair of the contact points. Regardless of the flow direction of an electric current flowing through the movable contactor 82 along the longitudinal direction of the movable contactor 82, the arc currents generated in the respective pairs of the contact points are drawn out away from each other.
The arc currents generated between the contact points when the movable contact points 821 comes into contact and out of contact with the fixed contact points 811 are drawn out by the magnetic fields generated from the permanent magnets 9, whereby the arc is cut off.
In the contact device disclosed in Japanese Patent Application Publication No. 2004-71512, however, the permanent magnets 9 are arranged in an opposing relationship with the respective end surfaces of the movable contactor 82 along the side-by-side arrangement direction of the movable contact points 821. This poses a problem in that the size of the contact device grows larger in the side-by-side arrangement direction of the movable contact points 821.
In the contact devices disclosed in Japanese Patent Application Publication Nos. 2004-71512 and 2008-226547, the permanent magnets 9 are arranged at the longitudinal opposite end sides of the contact point block 8. Therefore, the magnetic gap between the permanent magnets 9 becomes larger and the amount of magnetic fluxes leaked in the magnetic gap gets increased. For that reason, the force acting to draw out the arcs generated between the contact points is weakened. This may make it impossible to obtain high enough arc cutoff performance.
As one method of enhancing the arc cutoff performance in the contact devices stated above, it is thinkable to increase the size of the permanent magnets 9. In that case, however, there are posed problems such as an increase in the cost of the permanent magnets 9 and an increase in the size of the contact devices.